I found it relatively straightforward, what are you using? I'm on Ubuntu 20 LTS with Virutalmin LEMP stack. I removed MySQL and installed MariaDB made a syslink for Webmin, removed PHP whatever version was pre-installed (7.3?) and installed 8.0. Made a server for the forum in virtualmin (e.g. discuss.example.com), installed Composer, installed Flarum.
Once it's installed all you have to do to make it live is set the directory and file permissions correctly, and edit the server configuration file (again this can be done in the webmin control panel easily). You need to change the path of the server from (example): /home/discuss/public_html to /home/discuss/flarum/public and you can delete the public_html directory as well obviously. I think all I had to do after that was install the correct PHP extensions and then set the PHP settings right (you can edit those files in the webmin control panel), it gives you a html page that tells you what settings you need to change before your system is ready it's not very complicated.
I basically just followed this guide, but you need to know instinctively what you need to modify in the steps for your system, it'll depend on your OS, control panel, and webserver (NGINX or Apache). If you have a live-server already with CentOS 8 be aware you need to to a live-upgrade to AlmaLinux as soon as possible as Redhat betrayed all the users.
